Dialysis apparati are well known, and it is likewise well known that an essential feature of such an apparatus is the dialyzer unit in which the blood to be treated is brought into contact with one face of a semi-permeable membrane while the other face is brought into contact with a dialysate.
Most dialyzers now known or utilized are of the so-called "flow-through" type wherein blood is introduced into the treatment area through one conduit and, after treatment, discharged from the unit through a separate conduit. For such apparatus, the blood is commonly withdrawn from the patient through an artery or arterialized vein with the treated blood being then pumped back into the patient through a vein.
More recently, a reciprocating dialyzer has been suggested wherein the blood is introduced into the blood treatment area and then discharged, after treatment, through the same conduit as utilized for introduction of the blood into the blood treatment area. Such a dialyzer is shown in U.S. Pat. No. 4,071,444, wherein the blood is introduced into the blood treatment area, formed by a pair of thin semi-permeable membranes, through a central opening with dialysate being introduced into the unit for membrane contact at the periphery of the unit.
An important advantage of the reciprocating dialyzer is that it may be used with a suspension of sorbent in the dialysate. The sorbent keeps the concentration of toxic substances low in the dialysate, and thereby facilitates mass transfer across the membranes, as described in U.S. patent application Ser. No. 104,016, filed by S. R. Ash on Dec. 17, 1979, and entitled "Dialysis Material and Method For Removing Uremic Substances In An Artificial Kidney." With the use of sorbent suspension, the need for a large volume of rapidly flowing dialysate is obviated, and a portable dialyzer becomes a reality. A disadvantage of the suspension, however, is that, as a thick slurry, it is difficult to maintain in a unidirectional flow pattern through small orifices. Therefore, special attention must be made to the orifices and flow channels of any spacers or membrane limiters in the reciprocating dialyzer.